The concept of topocatheter extension to the standard angiographic catheter to facilitate entry into small and tortuous vesels involves the production of a high strength thin walled tube that can be easily turned inside out. When the thin wall extension is exposed to negative pressure inside the catheter it first collapses and then inverts itself until it lines the distal end of the catheter. Pressure inside the catheter causes the lining to form a valve and shut so that flow can only occur by again inverting the thin wall tube. When the thin wall tube everts it rolls onto the inside of the vessel wall with no friction so that it can enter tortuous vessels with ease. A 12 cm extension on a No. 7F catheter tapered to 1mm is typical. A triangular tapered shape reduces self inteference of the thin wall extension.